Steroid hormones play complex roles in regulating physiological and developmental functions as diverse as sodium and water balance to mammalian sexual differentiation, insect moulting, and control of cell and tumor proliferation. Despite the widespread use of steroids as therapeutic agents the mechanisms by which they exert their effects are only dimly understood. Twenty-five years have elapsed since the discovery of steroid receptors and only now, for example, are we able to obtain a glimpse at the molecular architecture of these fascinating proteins. Application of sophisticated biochemical and molecular biological techniques has led to the conclusion that steroid receptors must act, at least in part, by regulating the transcription of specific genes within target cells; the mechanisms by which genes are of targeted for response in a tissue-specific manner and the mechanisms by which the transcription machinery is itself regulated by steroid receptors remain obscure. A particular emphasis of this meeting, which will run concurrently with a symposium on "Growth Regulation of Cancer", is the role that steroid hormones play in the proliferation of various neoplasms. With the recent discovery that steroid receptors share homology with a viral oncogene and the ever-increasing attention being paid to the interaction between steroids and growth factor receptors and oncogenes, this meeting should be of particular interest to investigators in the field of steroid action as well as those with a broad interest in cell biology, development, and growth control. The expanded use of steroid and steroid antagonists in the therapy of certain tumors provides additional impetus for attention to this field by clinical oncologists.